1. Field of the Invention
The present invention generally relates to movable table systems, and particularly relates to movable table systems to be incorporated into various machines used for various purposes, for example, a ruling engine, and the like.
2. Description of the Prior Art
Generally, a conventional movable table system incorporated in a precision machine for precise processing or measurement so as to be used to convey an article, such as an object to be processed or measured, a cutting tool, a measuring instrument, or the like, to a predetermined position has such a basic structure as diagrammatically shown in FIG. 4. As seen in the drawing, a movable table having a mass of m is supported on guides 2 such that the guides 2 restrict the movement of the movable table 1 in the direction perpendicular to the surface of the paper of drawing while permitting the movable table 1 to reciprocate without friction in the direction parallel to the surface of the paper of drawing. The guides 2 are constituted, for example, by aerosliders and mounted on a base 3 which is in turn mounted on a foundation 4 through vibration absorbers 5 and 5'. A direct-acting type driving means, for example, a linear servomotor (not shown), is provided between the base 3 and the movable table 1 so as to move the movable table 1 left or right in the drawing relative to the base 3 when the linear servomotor is energized.
The thus arranged conventional movable table system has such problems in its operation as follows.
In the conventional movable table system of FIG. 4, when the movable table 1 is moved, for example, left in the drawing parallel to the surface of the paper of drawing, the center of gravity of the system as a whole moves left by an amount corresponding to the distance of movement of the movable table 1, so that the forces acting on the respective vibration absorbers 5 and 5' change. That is, in this case, the left vibration absorber 5 sinks a little while the right vibration absorber 5' comes up slightly, so that the system inclines as a whole.
Generally, it is necessary to reduce the spring constant of each of the vibration absorbers 5 and 5' in order to cause the vibration absorbers to cut off low-frequency vibrations. However, if the spring constant is reduced the responsiveness of the vibration absorbers 5 and 5' becomes poor and makes it impossible to follow the change in position of the center of gravity of the system.
With respect to almost all precision machines, inclination of a movable table incorporated in the precision machine has a great influence upon precision, and therefore vibration absorbers cannot be additionally provided to such a movable table system in which the center of gravity of the system varies as a whole.
Furthermore, in the conventional movable table system, when the linear servomotor is energized to thereby move the movable table 1, for example, left in the drawing at an acceleration .alpha..sub.1, reactive force F=m.alpha..sub.1 acts on the base 3 in the direction opposite to the movement of the movable table 1. The force F is then transmitted onto the foundation 4 through the vibration absorbers 5 and 5'. Although the acceleration .alpha..sub.1 can be increased to the order of exceeding 1 G which is the acceleration of gravity by the use of the linear servomotor, the force acting on the foundation 4 becomes greater in this case. Accordingly, there occurs such a problem that the vibrations cannot be suppressed unless both the strength and mass of the foundation 4 are made considerably large.
In other words and in more detail, in the case where the conventional movable table system is incorporated into a very high precision machine such as a ruling engine, it is necessary to make the base 3 sufficiently heavy as compared with the movable table 1 and to make the acceleration/deceleration of the movable table 1 sufficiently small, in order to suppress the vibrations of the movable table 1 in an accelerating/decelerating operation.
In addition, in the case where the movable table system is incorporated, for example, in a wire bonder used in a process of manufacturing integrated circuits, the movable table 1 is moved at a large acceleration/deceleration so that it may be a source of vibrations in itself to thereby make it difficult to effect high-precise positioning of the table per se.